It is known to attack undesirable cells or growths in tissue directly to kill the growth or stop its spread. Apparatus and systems have been developed to ablate such growths through application of heat or cold, injection of chemicals, or other treatments. For example, applying sufficient heat to part or all of a cancerous or pre-cancerous growth, or injecting it with a localized toxin, kills the cells and so slows or stops the growth or spread of the problem cells. The dead cells can be collected, or the body's own mechanisms for clearing dead tissue can be allowed to eliminate those cells. Such a treatment is generally less traumatizing, painful and difficult than cutting out and removing live tissue from the body.
Injection of a toxin carries substantial risk of harming adjacent or remote tissues by absorption of the toxin. Devices for precise local application of heat or cold are generally very expensive and technically complex. In the case of heat ablation, the expense and complexity generally result from the sources of the applied heat. Radio-frequency (RF) energy, microwave energy and laser energy are common sources, and the devices to generate such energy are quite expensive. Additionally, such energy must be carefully focused on a heat-receiving medium, which may be either the tissue itself or a fluid reservoir or other medium that is heated by the energy and placed in contact with the tissue. The energy must be carefully shielded so as not to affect other tissues in the patient, or persons or equipment in proximity to the patient.
Other systems using chemical reactions in tissue treatment have been proposed. In International Publication No. WO2008/106357 A1, there is shown a device that moves an acid and a base to and out of a needle and into or adjacent to tissue. The needle has openings at the end so that the chemicals exit, emitting heat as they remain along or soak into tissue. The inventor views a drawback to this system in the emission of the chemicals into the tissue. A substantial risk of absorption of relatively concentrated acid or base into the target tissue and transmission to other tissues or the blood stream exists. The ability of tissues to take up such liquids suggests that that risk is quite high. There is also the risk that the emission of such chemicals from a needle in tissue will flow away from the target, missing it partially or completely.
U.S. Pat. No. 4,796,622 (Lu et al.) and U.S. Pat. No. 6,824,555 (Towler et al.) disclosed devices that use hydrogen and oxygen gases in the presence of a metal catalyst to generate heat. These devices are also expensive, at least because of the metals (e.g. palladium) required as catalysts in order for them to operate. Initial heating of part of the device by electricity also adds to the complexity and cost of these systems. The requirements for safe handling and supply connection of potentially explosive oxygen and hydrogen gases are substantial. The extra electrolysis structure suggested in U.S. Pat. No. 6,824,555 to provide the hydrogen and oxygen gases also adds to complexity and expense of a system. Gases' natural occupation of the entire volume they are allotted, with the pressure variations gases can undergo, means that constant gas flow and consistent pressure are needed in these systems in order to both maintain the reaction and to prevent it from propagating back toward the source of the gases. Openings from the devices are also needed as part of the gas flow path to vent unused gas and/or by-products and thereby maintaining the necessary constant gas pressure.
Accordingly, there is a need for a less expensive and less complex system for ablating tissues, while maintaining safety for the patient and others. The present disclosure meets this need.